The field of the invention is compact unitary ice cube makers with refrigerated compartments, and more particularly, to control systems therefor.
Compact ice makers include an automatic ice making unit for maintaining a ready supply of ice cubes. Such ice automatic ice making units are generally known, and include an ice mold and means for filling the ice mold with water, usually via a solenoid controlled water valve. It should be understood that the term "ice cube" is used to refer to any shape, not limited to perfect cubes. Most ice molds for automatic ice making produce "half moon" shaped wedges for ease in freezing and harvesting.
When the water freezes in the ice mold, its temperature drops below freezing. A single sensor located on the ice mold is used to sense the ice mold temperature. When that temperature falls below a predetermined setpoint temperature, the ice in the mold is frozen and ready to be harvested. The ice is typically harvested by a gear reduction, high torque motor which either drives the ice out of the mold, or otherwise rotates or twists the mold to release the ice. An ice mold heater is commonly employed during the harvesting operation to produce localized melting at the interface between the ice and the mold, thereby facilitating release of the ice. Normally, a refrigeration compressor is run constantly until the ice harvest is initiated. Then the compressor is shut off during the ice harvest cycle so as not to oppose the ice mold heater. After the harvest cycle is complete, the compressor is restarted to freeze another batch of ice.
Compact unitary ice cube makers of the above described type are commonly used in homes and small offices to provide for both the production of ice cubes and the refrigerated storage of other items, for example, beverages and perishable foodstuffs, at a temperature above freezing in a "fresh food compartment". When the ice maker also includes a fresh food compartment, the freezer section with the automatic ice making unit is located in a separate section adjoining the fresh food compartment.
In such applications, e.g. ice maker with fresh food compartment, the production of ice at a maximum rate is the controlling factor for the refrigeration system. In other words, the refrigeration system is controlled by the ice making mechanism, or process, as described above. The compressor operates continuously until the ice in the mold is frozen. Then, the compressor is shut off while the ice is harvested. After the harvest, the compressor is again engaged until the next batch of ice is frozen.
If ice is withdrawn from the reservoir on the average at a rate approximating the ice production capacity, the above described cycle for control of the compressor repeats indefinitely. If ice is not used as fast as it is produced, it accumulates in a reservoir, or bin. A switch is usually provided to detect a full bin condition, in which case ice harvesting is suppressed until the full bin condition is relieved.
One problem associated with prior ice makers with fresh food compartments of the type just described is that the temperature of the fresh food compartment is subject to wide variation, especially towards warmer temperatures. The only source of cooling for the fresh food compartment is the freezer compartment, specifically an evaporator in contact with the ice mold used to produce the ice. This is usually enough to maintain the ice stored in the bin in a frozen condition. Extraneous heat losses, for example opening the ice maker door, can cause the temperature in the fresh food compartment to rise even though ice is still being satisfactorily produced in the automatic ice making unit. As stated above, the control system for such prior ice makers is adapted of optimum ice production without regard to the temperature in the fresh food compartment, and so the temperature in the fresh food compartment is essentially uncontrolled
One prior solution addressing this problem is described in U.S. Pat. No. 3,788,089, in which a system of baffles and apertures are placed so as to achieve a cooling air exchange between the freezer and fresh food compartment which serves to moderate the temperature of the latter. While this approach is generally satisfactory, the lack of refrigeration during ice harvesting and other variables, for example the number of door openings and the amount and temperature of the articles placed in the fresh food compartment, may result in temporarily warmer temperatures in the fresh food compartment.